Spin element and magnetic memory

ABSTRACT

This spin element includes: a current-carrying part that extends in a first direction; and an element part that is laminated on one surface of the current-carrying part, wherein the current-carrying part includes a first wiring and a second wiring in order from a side of the element part, and wherein both of the first wiring and the second wiring are metals and temperature dependence of resistivity of the first wiring is larger than temperature dependence of resistivity of the second wiring in at least a temperature range of −40° C. to 100° C.

The present invention relates to a spin element and a magnetic memory.

This is a Division of application Ser. No. 16/756,262 filed Apr. 15,2020, which in turn is a National Stage Application of PCT/JP2019/004840filed on Feb. 2, 2019, which claims priority to PCT/JP2018/037721 filedon Oct. 10, 2018, and Japanese Patent Application No. 2018-027130 filedon Feb. 19, 2018. The disclosure of the prior applications is herebyincorporated by reference herein in its entirety.

TECHNICAL FIELD Background Art

A giant magnetoresistance (GMR) element including a multilayer film of aferromagnetic layer and a non-magnetic layer and a tunnelmagnetoresistance (TMR) element using an insulating layer (a tunnelbarrier layer and a barrier layer) for a non-magnetic layer are known asa magnetoresistance effect element. Generally, the TMR element has ahigher element resistance and a higher magnetoresistance (MR) ratio thanthose of the GMR element. For this reason, TMR elements have beengaining attention as elements for magnetic sensors, high-frequencycomponents, magnetic heads, and magnetic random access memories (MRAMs).

In recent years, magnetization reversal using a pure spin currentgenerated by a spin-orbit interaction has been gaining attention (forexample, Non-Patent Document 1). A spin-orbit torque (SOT) is induced bya pure spin current caused by a spin-orbit interaction or a Rashbaeffect in an interface between different materials. A current forinducing an SOT in a magnetoresistance effect element flows in adirection intersecting a laminating direction of the magnetoresistanceeffect element. That is, there is no need for a current to flow in alaminating direction of the magnetoresistance effect element, and suchmagnetoresistance effect elements can be expected to have a longerlifespan.

PRIOR ART DOCUMENTS Non-Patent Document

-   Non-Patent Document 1: S. Fukami, T. Anekawa, C. Zhang and H. Ohno,    Nature Nano Tec (2016). DOI: 10.1038/NNANO.2016.29.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An element that uses a magnetoresistance effect is used for variousapplications and operation guarantee in a wide temperature range isrequired. In a spin element using an SOT, the magnitude of the magneticanisotropy energy of the ferromagnetic material, the resistivity of thewiring, and the like change depending on the temperature. For thatreason, there is a need for a spin element using an SOT that operatesstably even when the operating temperature range changes. Further, sucha situation is not limited to the spin-orbit-torque magnetizationrotational element, but the same applies to a magnetic domain walldisplacement type magnetic recording element using a movement of amagnetic domain wall.

The present invention has been made in view of the above-describedcircumstances and an object of the present invention is to provide aspin element and a magnetic memory with low temperature dependence.

Solutions for Solving the Problems

The present inventors have carried out a careful examination and foundthat temperature dependence of a spin element can be reduced by forminga current-carrying part to have a lamination structure of a first wiringand a second wiring and changing a distribution ratio of a currentflowing in the first wiring and the second wiring for each temperaturerange.

The present invention provides the following solutions in order to solvethe above-described problems.

(1) A spin element according to a first aspect includes: acurrent-carrying part that extends in a first direction; and an elementpart that faces the current-carrying part, wherein the current-carryingpart includes a first wiring and a second wiring in order from a side ofthe element part, and wherein both of the first wiring and the secondwiring are metals and temperature dependence of resistivity of the firstwiring is larger than temperature dependence of resistivity of thesecond wiring in at least a temperature range of −40° C. to 100° C.

(2) A spin element according to a second aspect includes: acurrent-carrying part that extends in a first direction; and an elementpart that faces the current-carrying part, wherein the current-carryingpart includes a first wiring and a second wiring in order from a side ofthe element part, and wherein the first wiring is a metal and the secondwiring is a semiconductor.

(3) A spin element according to a third aspect includes: acurrent-carrying part that extends in a first direction; and an elementpart that faces the current-carrying part, wherein the current-carryingpart includes a first wiring and a second wiring in order from a side ofthe element part, and wherein the first wiring is a metal and the secondwiring is a topological insulator.

(4) A spin element according to a fourth aspect includes: acurrent-carrying part that extends in a first direction; and an elementpart that faces the current-carrying part, wherein the current-carryingpart includes a first wiring and a second wiring in order from a side ofthe element part, and wherein the first wiring is a semiconductor andthe second wiring is a topological insulator.

(5) In the spin element according to the above-described aspect, thecurrent-carrying part may be a spin-orbit torque wiring configured toapply a spin-orbit torque to a magnetization of the first ferromagneticlayer so as to rotate the magnetization of the first ferromagnetic layerand the element part may include a first ferromagnetic layer.

(6) In the spin element according to the above-described aspect, thecurrent-carrying part may be a spin-orbit torque wiring configured toapply a spin-orbit torque to magnetization of the first ferromagneticlayer so as to rotate the magnetization of the first ferromagnetic layerand the element part may include a first ferromagnetic layer, anon-magnetic layer, and a second ferromagnetic layer in order from aposition near the current-carrying part.

(7) In the spin element according to the above-described aspect, thecurrent-carrying part may be a magnetic recording layer including amagnetic domain wall and the element part may include a non-magneticlayer and a first ferromagnetic layer in order from a position near themagnetic recording layer.

(8) In the spin element according to the above-described aspect, thesecond wiring may contain one or more alloys selected from a groupconsisting of chromel, constantan, nichrome, platinum rhodium, manganin,and alumel.

(9) In the spin element according to the above-described aspect, thefirst wiring may contain at least one element selected from a groupconsisting of tungsten, bismuth, rubidium, tantalum, molybdenum,rhodium, and tin and the second wiring may contain at least one elementselected from a group consisting of iridium, platinum, and palladium.

(10) In the spin element according to the above-described aspect, thefirst wiring may contain a non-magnetic metal having a large atomicnumber of 39 or more and having d electrons or f electrons in anoutermost shell.

(11) In the spin element according to the above-described aspect, thefirst wiring may have a thickness equal to or smaller than a spindiffusion length of an element constituting the first wiring.

(12) A magnetic memory according to a fifth aspect includes a pluralityof the spin elements according to the above-described aspect.

Effects of the Invention

According to the spin element of the above-described aspect, thetemperature dependence can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of a spin-orbit-torquemagnetization rotational element according to a first embodiment.

FIG. 2A is a diagram schematically showing an example of temperaturedependence of resistivity of a first wiring and a second wiring of thespin-orbit-torque magnetization rotational element according to thefirst embodiment.

FIG. 2B is a diagram schematically showing an example of the temperaturedependence of the resistivity of the first wiring and the second wiringof the spin-orbit-torque magnetization rotational element according tothe first embodiment.

FIG. 2C is a diagram schematically showing an example of the temperaturedependence of the resistivity of the first wiring and the second wiringof the spin-orbit-torque magnetization rotational element according tothe first embodiment.

FIG. 3 is a schematic cross-sectional view of a spin-orbit-torquemagnetization rotational element according to a second embodiment.

FIG. 4A is a diagram schematically showing an example of temperaturedependence of resistivity of a first wiring and a second wiring of thespin-orbit-torque magnetization rotational element of the secondembodiment.

FIG. 4B is a diagram schematically showing an example of the temperaturedependence of the resistivity of the first wiring and the second wiringof the spin-orbit-torque magnetization rotational element according tothe second embodiment.

FIG. 4C is a diagram schematically showing an example of the temperaturedependence of the resistivity of the first wiring and the second wiringof the spin-orbit-torque magnetization rotational element according tothe second embodiment.

FIG. 5 is a schematic cross-sectional view of a spin-orbit-torque typemagnetoresistance effect element according to a third embodiment.

FIG. 6 is a schematic cross-sectional view of a magnetic domain walldisplacement type magnetic recording element according to a fourthembodiment.

FIG. 7 is a diagram schematically showing a magnetic memory according toa fifth embodiment.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, preferred examples of the present invention will bedescribed in detail by appropriately referring to the drawings. In thedrawings used in the following description, characteristic parts areenlarged for convenience of description in order to easily understandthe characteristics of the present invention and hence the dimensionalratio of each component may be different from the actual one. Thematerials, dimensions, and the like exemplified in the followingdescription are merely examples and the present invention is not limitedthereto and can be implemented with appropriate modifications within arange in which the effects of the present invention are exhibited.

First Embodiment

(Spin-Orbit-Torque Magnetization Rotational Element)

FIG. 1 is a schematic cross-sectional view showing a spin-orbit-torquemagnetization rotational element according to a first embodiment. Thespin-orbit-torque element is an example of a spin element. Aspin-orbit-torque magnetization rotational element 100 shown in FIG. 1includes a first ferromagnetic layer 10 and a spin-orbit torque wiring20. The spin-orbit torque wiring is an example of a current-carryingpart. The first ferromagnetic layer 10 is an example of an element part.The first ferromagnetic layer 10 faces the spin-orbit torque wiring 20.“Facing” means a relationship of facing each other and two layers may bein contact with each other or another layer may be interposedtherebetween.

Hereinafter, a description will be made on the assumption that a firstdirection in which the spin-orbit torque wiring 20 extends is defined asthe x direction, a direction orthogonal to the first direction within aplane where the spin-orbit torque wiring 20 exists is defined as the ydirection, and a direction orthogonal to the x direction and the ydirection is defined as the z direction. In FIG. 1 , the z directionmatches the laminating direction of the first ferromagnetic layer 10 andthe thickness direction of the spin-orbit torque wiring 20.

<First Ferromagnetic Layer>

The first ferromagnetic layer 10 functions by changing the direction ofmagnetization M₁₀. The axis of easy magnetization of the firstferromagnetic layer 10 shown in FIG. 1 is the z direction. The firstferromagnetic layer 10 is a perpendicular magnetization film in whichthe magnetization M₁₀ is oriented in the z direction. The firstferromagnetic layer 10 may be an in-plane magnetic film in which themagnetization M₁₀ is oriented in the in-plane direction of the xy plane.

A ferromagnetic material, in particular, a soft magnetic material can beapplied to the first ferromagnetic layer 10. For the first ferromagneticlayer 10, for example, metals selected from a group consisting of Cr,Mn, Co, Fe, and Ni, alloys containing one or more of these metals, andalloys containing one or more of these metals and at least one or moreelements of B, C and N can be used. Specifically, Co—Fe, Co—Fe—B, andNi—Fe can be exemplified.

Further, a Heusler alloy such as Co₂FeSi may be used for the firstferromagnetic layer 10. The Heusler alloy contains an intermetalliccompound with a chemical composition of XYZ or X₂YZ. X represents atransition metal element of the Co, Fe, Ni, or Cu group or a noble metalelement on the periodic table. Y represents a transition metal of theMn, V, Cr or Ti group or an element type of X. Z represents a typicalelement of Group III to Group V. Examples of the Heusler alloys include,for example, Co₂FeSi, Co₂FeGe, Co₂FeGa, Co₂MnSi,Co₂Mn_(1-a)Fe_(a)Al_(b)Si_(1-b), Co₂FeGe_(1-c)Ga_(c), and the like.Heusler alloys have high spin polarization.

<Spin-Orbit Torque Wiring>

The spin-orbit torque wiring 20 extends in the x direction. Thespin-orbit torque wiring 20 includes a first wiring 21 and a secondwiring 22.

When a current flows to the spin-orbit-torque wiring 20, a spin currentis generated due to a spin Hall effect. The spin Hall effect is aphenomenon in which a spin current is induced in a direction orthogonalto the direction of a current based on a spin-orbit interaction when acurrent flows through a wiring. A mechanism in which a spin current isgenerated by the spin Hall effect will be described.

As shown in FIG. 1 , a current I flows in the x direction when apotential difference is applied to both ends of the spin-orbit torquewiring 20 in the x direction. When the current I flows in the spin-orbittorque wiring 20, each of a first spin S1 oriented in the y directionand a second spin S2 oriented in the −y direction is bent in a directionorthogonal to the current. A spin current is induced in a direction toeliminate the uneven distribution of the first spin and the second spin.

The normal Hall effect and the spin Hall effect are common in that themovement (moving) direction of the moving charges (electrons) is bent.However, in the normal Hall effect, when a charged particle moves in amagnetic field, the charged particle receives a Lorentz force and themovement direction is bent. On the other hand, in the spin Hall effect,electrons move only (a current flows only) in an environment where amagnetic field is absent and the direction in which the spin moves isbent by a spin-orbit interaction.

In a non-magnetic material (a material that is not a ferromagneticmaterial), the number of electrons of the first spin S1 is equal to thenumber of electrons of the second spin S2. Therefore, in the drawing,the number of electrons of the first spin S1 traveling in the zdirection is equal to the number of electrons of the second spin S2traveling in the −z direction. In this case, the flow of electrons iscanceled and the amount of current becomes zero. This spin currentwithout a current is particularly called a pure spin current.

If the electron flow of the first spin S1 is represented by J_(⬆), theelectron flow of the second spin S2 is represented by J_(⬇), and thespin current is represented by J_(S), this is defined asJ_(S)=J_(⬆)−J_(⬇). In FIG. 1 , Js as a pure spin current flows in the zdirection of the drawing. J_(S) is an electron flow having apolarization of 100%. When the first ferromagnetic layer 10 is allowedto contact the upper surface of the spin-orbit torque wiring 20, thepure spin current diffuses and flows into the first ferromagnetic layer10. That is, the spin is injected into the first ferromagnetic layer 10.

The spin-orbit torque wiring 20 includes at least a first wiring 21 anda second wiring 22. In the spin-orbit torque wiring 20, one or morelayers of wiring other than the first wiring 21 and the second wiring 22may be laminated.

The first wiring 21 is a wiring which is closest to the firstferromagnetic layer 10 in the spin-orbit torque wiring 20. The secondwiring 22 is a wiring which is located at a position farther from thefirst ferromagnetic layer 10 than the first wiring 21.

Both of the first wiring 21 and the second wiring 22 according to thefirst embodiment consist of a metal. The “metal” is not limited to asimple metal, but may be an alloy. Further, the term “consist of ametal” means that other materials such as impurities are allowed to becontained when the first wiring 21 and the second wiring 22 show ametallic behavior with respect to a temperature change. The metallicbehavior means a behavior in which a resistance value increases as thetemperature increases.

In the first wiring 21, the temperature dependence of resistivity islarger than the temperature dependence of resistivity of the secondwiring 22 in at least a temperature range of −40° C. to 100° C. The“temperature dependence of the resistivity” corresponds to a differencebetween the resistance value of the wiring at −40° C. and the resistancevalue of the wiring at 100° C. That is, a difference between theresistance value at −40° C. and the resistance value at 100° C. of thefirst wiring 21 is larger than a difference between the resistance valueat −40° C. and the resistance value at 100° C. of the second wiring 22.

FIGS. 2A to 2C schematically show the temperature dependence of theresistivity of the first wiring 21 and the second wiring 22. Aresistance value R₂₁ of the first wiring 21 and a resistance value R₂₂of the second wiring 22 may have any relationship of FIGS. 2A to 2C oncondition that the above-described relationship of the temperaturedependence is satisfied. FIG. 2A is a diagram showing a case in whichthe resistance value R₂₁ of the first wiring 21 and the resistance valueR₂₂ of the second wiring 22 are reversed at any temperature. FIG. 2B isa diagram showing a case in which the resistance value R₂₁ of the firstwiring 21 is always larger than the resistance value R₂₂ of the secondwiring 22 in a temperature range of −40° C. to 100° C. FIG. 2C is adiagram showing a case in which the resistance value R₂₁ of the firstwiring 21 is always smaller than the resistance value R₂₂ of the secondwiring 22 in a temperature range of −40° C. to 100° C.

The main configuration of the spin-orbit-torque wiring 5 of the firstwiring 21 is preferably a non-magnetic heavy metal. The heavy metalmeans a metal having a specific gravity of yttrium or more. It ispreferable that the non-magnetic heavy metal is a non-magnetic metalhaving a large atomic number of 39 or more and having d electrons or felectrons in the outermost shell. These non-magnetic metals have a largespin-orbit interaction that causes the spin Hall effect.

Electrons generally move in the direction opposite to the currentregardless of their spin direction. On the other hand, a non-magneticmetal of a large atomic number having d electrons or f electrons in theoutermost shell has a large spin-orbit interaction and a strong spinHall effect. Therefore, the electron movement direction depends on thedirection (orientation) of electron spin. Thus, the spin current J_(S)is likely to occur in such a non-magnetic heavy metal.

The second wiring 22 preferably contains one or more alloys selectedfrom a group consisting of chromel, constantan, nichrome, platinumrhodium, manganin, and alumel. These alloys have small temperaturedependence and a small change in resistance value with a temperaturechange.

Further, as a combination of the first wiring 21 and the second wiring22, each wiring preferably contains the following elements. The firstwiring 21 preferably contains at least one element selected from a groupconsisting of tungsten, bismuth, rubidium, tantalum, molybdenum,rhodium, and tin. The second wiring preferably contains at least oneelement selected from a group consisting of iridium, platinum, andpalladium.

The second wiring 22 also preferably contains a non-magnetic heavy metalin order to cause a spin Hall effect. It is preferable that both of thefirst wiring 21 and the second wiring 22 contain a heavy metal and havea configuration in which the above-described elements are combined. Withthis configuration, a large spin-orbit interaction can be generatedwhile the first wiring 21 and the second wiring 22 satisfy thepredetermined temperature dependence.

It is preferable that the thickness of the first wiring 21 is equal toor smaller than the spin diffusion length of an element constituting thefirst wiring 21. In the case where the thickness of the first wiring 21is sufficiently small, the spin generated in the second wiring 22 canreach the first ferromagnetic layer 10.

For example, the thickness of the first wiring 21 is preferably 0.25times or more and 2.0 times or less the thickness of the second wiring22 and is more preferably 0.5 times or more and 1.0 times or less thethickness of the second wiring 22.

When the thickness of the first wiring 21 and the thickness of thesecond wiring 22 satisfy the above-described relationship, a differencein resistivity between the first wiring 21 and the second wiring 22 doesnot become large. Further, since a current flowing to the spin-orbittorque wiring 20 can be decreased, the installation area of thespin-orbit-torque magnetization rotational element or the size of thetransistor can be decreased.

Further, the spin-orbit torque wiring 20 may further contain a magneticmetal. The magnetic metal represents a ferromagnetic metal orantiferromagnetic metal. When a small amount of a magnetic metal iscontained in a non-magnetic metal, this metal becomes a scatteringfactor of spins. When the spin is scattered, the spin-orbit interactionis enhanced and the efficiency of generating a spin current with respectto the current increases.

Meanwhile, when the added amount of the magnetic metal is too large, thegenerated spin current is scattered by the added magnetic metal. As aresult, the effect of reducing the spin current may be increased. Forthat reason, it is preferable that the molar ratio of the magnetic metalto be added is sufficiently smaller than the total molar ratio of theelements constituting the spin-orbit-torque wiring. It is preferablethat the molar ratio of the magnetic metal to be added is 3% or less ofthe whole.

The spin-orbit torque wiring 20 may further contain a topologicalinsulator. The topological insulator is a substance in which the insideof the substance is an insulator or a high-resistance substance, but aspin-polarized metal state occurs in its surface. An internal magneticfield is generated in the topological insulator due to the spin-orbitinteraction. Therefore, a new topological phase appears due to theeffect of the spin-orbit interaction even in the case where an externalmagnetic field is absent. The topological insulator can generate a purespin current with high efficiency due to a strong spin-orbit interactionand breaking of inversion symmetry at an edge.

Preferred examples of the topological insulator include SnTe,Bi_(1.5)Sb_(0.5)Te_(1.7)Se_(1.3), TlBiSe₂, Bi₂Te₃, Bi_(1-x)Sb_(x), and(Bi_(1-x)Sbx)₂Te₃. These topological insulators can generate a spincurrent with high efficiency.

(Function of Spin-Orbit-Torque Magnetization Rotational Element)

The magnetic anisotropy energy of the first ferromagnetic layer 10 at alow temperature is larger than the magnetic anisotropy energy of thefirst ferromagnetic layer 10 at a high temperature. That is, themagnetization M₁₀ of the first ferromagnetic layer 10 is difficult torotate at a low temperature and the magnetization M₁₀ of the firstferromagnetic layer 10 easily rotates at a high temperature. In order torotate the magnetization M₁₀ of the first ferromagnetic layer 10, it isnecessary to inject more spins from the spin-orbit torque wiring 20 at alow temperature rather than a high temperature.

As shown in FIGS. 2A to 2C, the resistance values R₂₁ and R₂₂ of thefirst wiring 21 and the second wiring 22 at a low temperature (forexample, −40° C.) are smaller than the resistance values R₂₁ and R₂₂ ofthe first wiring 21 and the second wiring 22 at a reference temperature(for example, a room temperature). For that reason, in the case wherethe wiring is connected to a constant voltage source, the amount of thecurrent flowing in the spin-orbit torque wiring 20 at a low temperaturebecomes larger than that at the reference temperature. When the currentdensity of a current I flowing in the spin-orbit torque wiring 20increases, more spins are injected into the first ferromagnetic layer10.

Further, in the first wiring 21, the temperature dependence of theresistivity is larger than the temperature dependence of the resistivityof the second wiring 22 in at least a temperature range of −40° C. to100° C. It can be considered that the current I flowing in thespin-orbit torque wiring 20 branches to the first wiring 21 and thesecond wiring 22. The amount of the current branching to the firstwiring 21 increases as the temperature decreases.

The first wiring 21 is located on the side of the first ferromagneticlayer 10 in relation to the second wiring 22. That is, the first wiring21 is closer to the first ferromagnetic layer 10 than the second wiring22. For that reason, when the amount of current branching to the firstwiring 21 increases, more spins are efficiently injected into the firstferromagnetic layer 10.

On the contrary, the resistance values R₂₁ and R₂₂ of the first wiring21 and the second wiring 22 at a high temperature (for example, 100° C.)are larger than the resistance values R₂₁ and R₂₂ of the first wiring 21and the second wiring 22 at a reference temperature (for example, a roomtemperature). For that reason, in the case where the wiring is connectedto a constant voltage source, the amount of the current flowing in thespin-orbit torque wiring 20 at a high temperature becomes smaller thanthat at the reference temperature. The amount of the current flowing inthe spin-orbit torque wiring 20 decreases and the amount of spinsinjected into the first ferromagnetic layer 10 decreases. However, sincethe magnetization stability of the first ferromagnetic layer 10decreases at a high temperature, the magnetization M₁₀ of the firstferromagnetic layer 10 rotates even when the amount of injected spinsdecreases.

Further, the resistance value R₂₂ of the second wiring 22 is hardlyinfluenced by a temperature change. For that reason, the amount ofcurrent branching to the second wiring 22 at a high temperature islikely to increase compared to the first wiring 21. As the amount ofcurrent branching to the second wiring 22 increases at a hightemperature, the amount of current branching to the first wiring 21decreases relatively. Since the amount of current branching to the firstwiring 21 near the first ferromagnetic layer 10 decreases, the amount ofspins injected into the first ferromagnetic layer 10 decreases.

In the spin-orbit torque wiring 20, a ratio between the amount ofcurrent branching to the first wiring 21 and the amount of currentbranching to the second wiring 22 automatically changes in response to atemperature. Even in the case where a constant voltage is applied to thespin-orbit torque wiring 20, the amount of spins injected into the firstferromagnetic layer 10 changes in response to the stability of themagnetization M₁₀ of the first ferromagnetic layer 10.

As described above, the stability of the magnetization M₁₀ of the firstferromagnetic layer 10 is different. That is, the stability of themagnetization M₁₀ of the first ferromagnetic layer 10 is low at a hightemperature and is high at a low temperature. Thus, in thespin-orbit-torque magnetization rotational element 100 according to theembodiment, the amount of spins injected into the first ferromagneticlayer 10 changes in response to a temperature. The amount of spinsinjected at a low temperature increases and the amount of spins injectedat a high temperature decreases. Even in the case where the spin-orbittorque wiring 20 is connected to a voltage source applying a constantvoltage, the operation is automatically compensated (guaranteed) inaccordance with the stability of the magnetization M₁₀ of the firstferromagnetic layer 10. That is, the spin-orbit-torque magnetizationrotational element 100 according to the embodiment can be used in a widetemperature range.

The spin-orbit-torque magnetization rotational element 100 according tothe embodiment does not require a thermometer for measuring an operatingtemperature, a control unit for controlling an applied voltage, and thelike. That is, the spin-orbit-torque magnetization rotational element100 according to the embodiment can be decreased in size.

Second Embodiment

FIG. 3 is a schematic cross-sectional view of a spin-orbit-torquemagnetization rotational element 101 according to a second embodiment.The spin-orbit-torque magnetization rotational element 101 shown in FIG.3 includes a first ferromagnetic layer 10 and a spin-orbit torque wiring25. The spin-orbit torque wiring 25 includes a first wiring 26 and asecond wiring 27. The spin-orbit-torque magnetization rotational element101 shown in FIG. 3 is different from the spin-orbit-torquemagnetization rotational element 100 shown in FIG. 1 in that a materialforming the second wiring 27 is a semiconductor. A description of thesame configuration as that of the spin-orbit-torque magnetizationrotational element 100 shown in FIG. 1 will be omitted.

The first wiring 26 is a metal and the second wiring 27 is asemiconductor. The “metal” means one having a metallic behavior withrespect to a temperature. Further, the “semiconductor” means one havinga semiconductor behavior with respect to a temperature. Thesemiconductor behavior means a behavior that a resistance valuedecreases as a temperature increases. Since the first wiring 26 and thesecond wiring 27 have a different behavior of a resistance value withrespect to a temperature change, the temperature dependence of theresistance value does not matter.

FIGS. 4A to 4C schematically show the temperature dependence of theresistivity of the first wiring 26 and the second wiring 27. Aresistance value R₂₆ of the first wiring 26 and a resistance value R₂₇of the second wiring 27 may have any relationship of FIGS. 4A to 4C.FIG. 4A is a diagram showing a case in which the resistance value R₂₆ ofthe first wiring 26 and the resistance value R₂₇ of the second wiring 27are reversed at any temperature. FIG. 4B is a diagram showing a case inwhich the resistance value R₂₆ of the first wiring 26 is larger than theresistance value R₂₇ of the second wiring 27 in a temperature range of−40° C. to 100° C. FIG. 4C is a diagram showing a case in which theresistance value R₂₆ of the first wiring 26 is smaller than theresistance value R₂₇ of the second wiring 27 in a temperature range of−40° C. to 100° C. Since the second wiring 27 which is a semiconductorgenerally has a higher resistance value than a resistance value of thefirst wiring 26 which is a metal, the relationship shown in FIG. 4C isobtained in many cases.

As shown in FIGS. 4A to 4C, the resistance value of the first wiring 26increases from a low temperature (for example, −40° C.) to a hightemperature (for example, 100° C.). Meanwhile, the resistance value ofthe second wiring 27 decreases from a low temperature (for example, −40°C.) to a high temperature (for example, 100° C.). For that reason, theamount of current branching to the first wiring 26 increases as thetemperature becomes lower and the amount of current branching to thesecond wiring 27 increases as the temperature becomes higher.

In the spin-orbit torque wiring 25, a ratio between the amount ofcurrent branching to the first wiring 26 and the amount of currentbranching to the second wiring 27 automatically changes in response to atemperature. Even in the case where a constant voltage is applied to thespin-orbit torque wiring 25, the amount of spins injected into the firstferromagnetic layer 10 changes in response to the stability of themagnetization M₁₀ of the first ferromagnetic layer 10.

As described above, in the spin-orbit-torque magnetization rotationalelement 101 according to the embodiment, the amount of spins injectedinto the first ferromagnetic layer 10 changes in response to atemperature. The amount of spins injected at a low temperature at whichthe stability of the magnetization M₁₀ of the first ferromagnetic layer10 is high increases. In contrast, the amount of spins injected at ahigh temperature at which the stability of the magnetization M₁₀ of thefirst ferromagnetic layer 10 is low decreases. Even in the case wherethe spin-orbit torque wiring 25 is connected to a voltage sourceconfigured to apply a constant voltage, the operation is automaticallycompensated (guaranteed) in accordance with the stability of themagnetization M₁₀ of the first ferromagnetic layer 10. That is, thespin-orbit-torque magnetization rotational element 101 according to theembodiment can be suitably used in a wide temperature range.

The spin-orbit-torque magnetization rotational element 101 according tothe embodiment does not require a thermometer for measuring an operatingtemperature, a control unit for controlling an applied voltage, and thelike. That is, the spin-orbit-torque magnetization rotational element101 according to the embodiment can be decreased in size.

The spin current magnetization rotational elements according to thefirst embodiment and the second embodiment can be applied to amagnetoresistance effect element as will be described later. However,the application is not limited to the magnetoresistance effect element,but can be applied to other applications. As other applications, forexample, the spin current magnetization rotational element can bedisposed in each pixel and used in a spatial light modulator thatspatially modulates incident light using a magneto-optical effect. Inthe magnetic sensor, the magnetic field applied to the axis of easymagnetization of the magnet may be replaced with an SOT in order toavoid the effect of hysteresis due to the coercivity of the magnet.

The spin current magnetization rotational element can be particularlyreferred to as a spin current magnetization reversing element when themagnetization is reversed.

Modified Example

Additionally, the spin-orbit-torque magnetization rotational elementaccording to the embodiment is not limited to the above-described one.

The first wirings 21 and 26 may be a metal and the second wirings 22 and27 may be a topological insulator.

The first wirings 21 and 26 may be a semiconductor and the secondwirings 22 and 27 may be a topological insulator.

Third Embodiment

<Spin-Orbit-Torque Type Magnetoresistance Effect Element>

FIG. 5 is a schematic cross-sectional view of a spin-orbit-torque typemagnetoresistance effect element 200 according to a third embodiment.The spin-orbit-torque type magnetoresistance effect element is anexample of a spin element. The spin-orbit-torque type magnetoresistanceeffect element 200 shown in FIG. 5 includes the spin-orbit-torquemagnetization rotational element 100, a non-magnetic layer 110, and asecond ferromagnetic layer 120. In FIG. 5 , the spin-orbit-torquemagnetization rotational element 100 according to the first embodimentis used as the spin-orbit-torque magnetization rotational element, butthe spin-orbit-torque magnetization rotational element 101 according tothe second embodiment may be used. A description of the sameconfiguration as that of the spin-orbit-torque magnetization rotationalelement 100 of the first embodiment will be omitted.

A laminated body (a functional unit 130) obtained by laminating thefirst ferromagnetic layer 10, the non-magnetic layer 110, and the secondferromagnetic layer 120 functions similarly to the normalmagnetoresistance effect element. The functional unit 130 is an exampleof an element part. The functional unit 130 functions by fixing themagnetization M₁₂₀ of the second ferromagnetic layer 120 in onedirection (for example, the −z direction) and relatively changing thedirection of the magnetization M₁₀ of the first ferromagnetic layer 10.In the case of applying to a coercivity-differed type (pseudo spin valvetype) MRAM, the coercivity of the second ferromagnetic layer 120 is madelarger than the coercivity of the first ferromagnetic layer 10. In thecase of applying to an exchange bias type (spin valve type) MRAM, themagnetization M₁₂₀ of the second ferromagnetic layer 120 is fixed byexchange coupling with the antiferromagnetic layer.

Further, in the functional unit 130, the functional unit 130 has thesame configuration as the tunneling magnetoresistance (TMR) element inthe case where the non-magnetic layer 110 consists of an insulator, andthe functional unit has the same configuration as the giantmagnetoresistance (GMR) element in the case where the non-magnetic layer110 consists of a metal.

The lamination configuration of the functional unit 130 can adopt thelamination configuration of the known magnetoresistance effect element.For example, each layer may include a plurality of layers or may furtherinclude other layers such as an antiferromagnetic layer for fixing themagnetization direction of the second ferromagnetic layer 120. Thesecond ferromagnetic layer 120 is referred to as a fixed layer or areference layer and the first ferromagnetic layer 10 is referred to as afree layer or a storage layer.

A known material can be used for the material of the secondferromagnetic layer 120. For example, a metal selected from a groupconsisting of Cr, Mn, Co, Fe, and Ni and an alloy containing at leastone of these metals and exhibiting ferromagnetism can be used. An alloycontaining one or more of these metals and at least one or more elementsof B, C, and N can also be used. Specifically, Co—Fe and Co—Fe—B areexemplified. Further, a Heusler alloy such as Co₂FeSi may be used forthe second ferromagnetic layer 120.

In order to increase the coercivity of the second ferromagnetic layer120 with respect to the first ferromagnetic layer 10, anantiferromagnetic material such as IrMn or PtMn may be used as amaterial in contact with the second ferromagnetic layer 120. Further, inorder to prevent the leakage magnetic field of the second ferromagneticlayer 120 from affecting the first ferromagnetic layer 10, a syntheticferromagnetic coupling structure may be employed.

A known material can be used for the non-magnetic layer 110.

For example, in the case where the non-magnetic layer 110 consists of aninsulator (in the case of a tunnel barrier layer), Al₂O₃, SiO₂, MgO,MgAl₂O₄, or the like can be used as the material thereof. In addition tothese, a material in which a part of Al, Si, and Mg is replaced with Zn,Be, or the like can also be used. Among these, MgO and MgAl₂O₄ arematerials capable of realizing a coherent tunneling. In the case wherethe non-magnetic layer 110 consists of a metal, Cu, Au, Ag, or the likecan be used as the material thereof. Further, in the case where thenon-magnetic layer 110 consists of a semiconductor, Si, Ge, CuInSe₂,CuGaSe₂, Cu(In, Ga)Se₂, or the like can be used as the material thereof.

The functional unit 130 may include other layers. For example, thefunctional unit may include a cap layer on a surface opposite to thenon-magnetic layer 110 in the second ferromagnetic layer 120.

The spin-orbit-torque type magnetoresistance effect element 200according to the third embodiment can record or read data by using achange in the resistance value of the functional unit 130 caused by adifference in relative angle between the magnetization M₁₀ of the firstferromagnetic layer 10 and the magnetization M₁₂₀ of the secondferromagnetic layer 120. Further, since the spin-orbit-torque typemagnetoresistance effect element 200 according to the third embodimentincludes the spin-orbit-torque magnetization rotational element 100, thespin-orbit-torque type magnetoresistance effect element can be suitablyused in a wide temperature range. Further, since the spin-orbit-torquetype magnetoresistance effect element 200 according to the thirdembodiment includes the spin-orbit-torque magnetization rotationalelement 100, the element can be decreased in size.

Fourth Embodiment

(Magnetic Domain Wall Displacement Type Magnetic Recording Element)

FIG. 6 is a schematic cross-sectional view of a magnetic domain walldisplacement type magnetic recording element 30 which is an example of aspin element according to the embodiment. The magnetic domain walldisplacement type magnetic recording element 30 shown in FIG. 6 includesan element part 51 and a magnetic recording layer 52. The magneticrecording layer 52 is an example of a current-carrying part. The elementpart 51 faces the magnetic recording layer (the current-carrying part)52.

<Element Part>

The element part 51 faces the current-carrying part. That is, theelement part is located on one surface of the magnetic recording layer52. The element part 51 includes a first ferromagnetic layer 51A and anon-magnetic layer 51B. For the first ferromagnetic layer 51A and thenon-magnetic layer 51B, the same layers as the second ferromagneticlayer 120 and the non-ferromagnetic layer 110 of the spin-orbit-torquetype magnetoresistance effect element 200 shown in FIG. 5 can be used.

<Magnetic Recording Layer>

The magnetic recording layer 52 extends in the x direction. The magneticrecording layer 52 includes a magnetic domain wall 52A therein. Themagnetic domain wall 52A is a boundary between a first magnetic domain52B and a second magnetic domain 52C having magnetizations in oppositedirections. In the magnetic domain wall displacement type magneticrecording element 30 shown in FIG. 6 , the first magnetic domain 52B hasmagnetization oriented in the +x direction and the second magneticdomain 52C has magnetization oriented in the −x direction.

The magnetic domain wall displacement type magnetic recording element 30records data in multi-values according to the position of the magneticdomain wall 52A of the magnetic recording layer 52. The data recorded inthe magnetic recording layer 52 is read as a change in the resistancevalue of the laminating direction of the first ferromagnetic layer 51Aand the magnetic recording layer 52. When the magnetic domain wall 52Amoves, the ratio between the first magnetic domain 52B and the secondmagnetic domain 52C of the magnetic recording layer 52 changes. Thedirection of the magnetization of the first ferromagnetic layer 51A isthe same as (parallel to) the direction of the magnetization of thefirst magnetic domain 52B and is opposite to (anti-parallel to) thedirection of the magnetization of the second magnetic domain 52C. Whenthe magnetic domain wall 52A moves in the x direction so that the areaof the first magnetic domain 52B in a portion overlapping the firstferromagnetic layer 51A when viewed from the z direction becomes large,the resistance value of the magnetic domain wall displacement typemagnetic recording element 30 decreases. In contrast, when the magneticdomain wall 52A moves in the −x direction so that the area of the secondmagnetic domain 52C in a portion overlapping the first ferromagneticlayer 51A when viewed from the z direction becomes large, the resistancevalue of the magnetic domain wall displacement type magnetic recordingelement 30 increases. The resistance value of the magnetic domain walldisplacement type magnetic recording element 30 is measured between anupper electrode electrically connected to the first ferromagnetic layer51A and an electrode provided in one end of the magnetic recording layer52.

The magnetic domain wall 52A moves by flowing current in the extensiondirection of the magnetic recording layer 52 or applying an externalmagnetic field. For example, when a current pulse is applied in the xdirection of the magnetic recording layer 52, the first magnetic domain52B spreads in the direction toward the second magnetic domain 52C andthe magnetic domain wall 52A moves in the direction toward the secondmagnetic domain 52C. That is, when the magnitude or the direction (the+x direction or the −x direction) of the current flowing in the magneticrecording layer 52 is set, the position of the magnetic domain wall 52Ais controlled and data is written to the magnetic domain walldisplacement type magnetic recording element 30.

The magnetic recording layer 52 includes a first wiring 53 and a secondwiring 54. The first wiring 53 is located at a position closer to theelement part 51 than the second wiring 54.

Each of the first wiring 53 and the second wiring 54 is a metal(magnetic material) having magnetism. “Metal” is not limited to a singlemetal, but may be an alloy. Further, the term “consist of a metal” meansthat other materials such as impurities are allowed to be contained whenthe first wiring 53 and the second wiring 54 show a metallic behaviorwith respect to a temperature change. The metallic behavior means abehavior in which a resistance value increases as the temperatureincreases.

In the first wiring 53, the temperature dependence of resistivity islarger than the temperature dependence of resistivity of the secondwiring 54 in at least a temperature range of −40° C. to 100° C. The“temperature dependence of the resistivity” corresponds to a differencebetween the resistance value of the wiring at −40° C. and the resistancevalue of the wiring at 100° C. That is, the temperature dependencecorresponds to a difference between the wiring resistance value of thefirst wiring 53 at −40° C. and the wiring resistance value thereof at100° C. That is, a difference between the resistance value at −40° C.and the resistance value at 100° C. of the first wiring 53 is largerthan a difference between the resistance value at −40° C. and theresistance value at 100° C. of the second wiring 54.

The first wiring 53 and the second wiring 54 preferably contain at leastone element selected from a group consisting of Co, Ni, Pt, Pd, Gd, Tb,Mn, Ge, and Ga. For example, a laminated film of Co and Ni, a laminatedfilm of Co and Pt, a laminated film of Co and Pd, a MnGa-based material,a GdCo-based material, and a TbCo-based material can be exemplified. Thematerials of the first wiring 53 and the second wiring 54 are selectedso as to satisfy the above-described “temperature dependence ofresistivity”. In addition, ferrimagnetic materials such as a MnGa-basedmaterial, a GdCo-based material, and a TbCo-based material have lowsaturation magnetization and can reduce a threshold current required formoving a magnetic domain wall. Further, a laminated film of Co and Ni, alaminated film of Co and Pt, and a laminated film of Co and Pd have alarge coercive force and can suppress the moving speed of the magneticdomain wall.

So far, a concrete example of a predetermined spin element has beendescribed. The spin-orbit-torque type magnetoresistance effect elements100 and 101 and the magnetic domain wall displacement type magneticrecording element 30 are common in that a write current flows throughthe current-carrying parts 20, 25, and 52 extending in a directionintersecting the element part (the first ferromagnetic layer 10, thefunctional unit 130, and the element part 51) during data writing. Thespin element is not limited to the spin-orbit-torque typemagnetoresistance effect elements 100 and 101 and the magnetic domainwall displacement type magnetic recording element 30 as long as a writecurrent flows to the current-carrying part extending in a directionintersecting the element part during data writing.

Fifth Embodiment

<Magnetic Memory>

FIG. 7 is a plan view of a magnetic memory 300 including the pluralityof spin-orbit-torque type magnetoresistance effect elements 200 (seeFIG. 5 ). FIG. 5 corresponds to a cross-sectional view in which thespin-orbit-torque type magnetoresistance effect element 200 is cut alonga plane A-A of FIG. 7 . In the magnetic memory 300 shown in FIG. 7 , thespin-orbit-torque type magnetoresistance effect elements 200 arearranged in a 3×3 matrix.

FIG. 7 shows an example of the magnetic memory and the number andarrangement of the spin-orbit-torque type magnetoresistance effectelements 200 are optional. Further, the magnetic memory may use thespin-orbit-torque magnetization rotational element 100 or the magneticdomain wall displacement type magnetic recording element 30 instead ofthe spin-orbit-torque type magnetoresistance effect element 200.

One of word lines WL1 to WL3, one of bit lines BL1 to BL3, and one ofread lines RL1 to RL3 are respectively connected to thespin-orbit-torque type magnetoresistance effect element 200.

By selecting the word lines WL1 to WL3 and the bit lines BL1 to BL3 towhich a current is applied, a current flows through the spin-orbittorque wiring 20 of an arbitrary spin-orbit-torque typemagnetoresistance effect element 200 so as to perform a writingoperation. By selecting the read lines RL1 to RL3 and the bit lines BL1to BL3 to which a current is applied, a current flows in the laminatingdirection of an arbitrary spin-orbit-torque type magnetoresistanceeffect element 200 so as to perform a reading operation. The word linesWL1 to WL3, the bit lines BL1 to BL3, and the read lines RL1 to RL3 towhich a current is applied can be selected by a transistor or the like.That is, this element can be used as the magnetic memory by reading dataof an arbitrary element from the plurality of spin-orbit-torque typemagnetoresistance effect elements 200.

As described above, the preferred embodiments of the present inventionhave been described in detail. However, the present invention is notlimited to the particular embodiment and various modifications andchanges can be made within the scope of the present invention describedin the appended claims.

EXPLANATION OF REFERENCE SIGNS

-   -   10 First ferromagnetic layer    -   20, 25 Spin-orbit torque wiring (current-carrying part)    -   21, 26 First wiring    -   22, 27 Second wiring    -   30 Domain wall displacement type magnetic recording element    -   40 Current-carrying part    -   51 Element part    -   51A First ferromagnetic layer    -   51B Second ferromagnetic layer    -   52A Magnetic domain wall    -   52B First magnetic domain    -   52C Second magnetic domain    -   100, 101 Spin-orbit-torque magnetization rotational element    -   110 Non-magnetic layer    -   120 Second ferromagnetic layer    -   130 Functional unit    -   200 Spin-orbit-torque type magnetoresistance effect element    -   300 Magnetic memory    -   M₁₀, M₁₂₀ Magnetization

1. A spin element comprising: a current-carrying part that extends in afirst direction; and an element part that faces the current-carryingpart, wherein the current-carrying part includes a first wiring and asecond wiring in order from a side of the element part, and wherein bothof the first wiring and the second wiring are metals and temperaturedependence of resistivity of the first wiring is larger than temperaturedependence of resistivity of the second wiring in at least a temperaturerange of −40° C. to 100° C.
 2. A spin element comprising: acurrent-carrying part that extends in a first direction; and an elementpart that faces the current-carrying part, wherein the current-carryingpart includes a first wiring and a second wiring in order from a side ofthe element part, and wherein the first wiring is a metal and the secondwiring is a topological insulator.
 3. A spin element comprising: acurrent-carrying part that extends in a first direction; and an elementpart that faces the current-carrying part, wherein the current-carryingpart includes a first wiring and a second wiring in order from a side ofthe element part, and wherein the first wiring is a semiconductor andthe second wiring is a topological insulator.
 4. The spin elementaccording to claim 1, wherein the current-carrying part is a spin-orbittorque wiring configured to apply a spin-orbit torque to magnetizationof the first ferromagnetic layer so as to rotate the magnetization ofthe first ferromagnetic layer, and wherein the element part includes afirst ferromagnetic layer.
 5. The spin element according to claim 1,wherein the current-carrying part is a spin-orbit torque wiringconfigured to apply a spin-orbit torque to magnetization of the firstferromagnetic layer so as to rotate the magnetization of the firstferromagnetic layer, and wherein the element part includes a firstferromagnetic layer, a non-magnetic layer, and a second ferromagneticlayer in order from a position near the current-carrying part.
 6. Thespin element according to claim 1, wherein the current-carrying part isa magnetic recording layer including a magnetic domain wall, and whereinthe element part includes a non-magnetic layer and a first ferromagneticlayer in order from a position near the magnetic recording layer.
 7. Thespin element according to claim 1, wherein the second wiring containsone or more alloys selected from a group consisting of chromel,constantan, nichrome, platinum rhodium, manganin, and alumel.
 8. Thespin element according to claim 1, wherein the first wiring contains atleast one element selected from a group consisting of tungsten, bismuth,rubidium, tantalum, molybdenum, rhodium, and tin, and wherein the secondwiring contains at least one element selected from a group consisting ofiridium, platinum, and palladium.
 9. The spin element according to claim4, wherein the first wiring contains a non-magnetic metal having a largeatomic number of 39 or more and having d electrons or f electrons in anoutermost shell.
 10. The spin element according to claim 4, wherein thefirst wiring has a thickness equal to or smaller than a spin diffusionlength of an element constituting the first wiring.
 11. A magneticmemory comprising: a plurality of the spin elements according toclaim
 1. 12. The spin element according to claim 2, wherein thecurrent-carrying part is a spin-orbit torque wiring configured to applya spin-orbit torque to magnetization of the first ferromagnetic layer soas to rotate the magnetization of the first ferromagnetic layer, andwherein the element part includes a first ferromagnetic layer.
 13. Thespin element according to claim 3, wherein the current-carrying part isa spin-orbit torque wiring configured to apply a spin-orbit torque tomagnetization of the first ferromagnetic layer so as to rotate themagnetization of the first ferromagnetic layer, and wherein the elementpart includes a first ferromagnetic layer.
 14. The spin elementaccording to claim 2, wherein the current-carrying part is a spin-orbittorque wiring configured to apply a spin-orbit torque to magnetizationof the first ferromagnetic layer so as to rotate the magnetization ofthe first ferromagnetic layer, and wherein the element part includes afirst ferromagnetic layer, a non-magnetic layer, and a secondferromagnetic layer in order from a position near the current-carryingpart.
 15. The spin element according to claim 3, wherein thecurrent-carrying part is a spin-orbit torque wiring configured to applya spin-orbit torque to magnetization of the first ferromagnetic layer soas to rotate the magnetization of the first ferromagnetic layer, andwherein the element part includes a first ferromagnetic layer, anon-magnetic layer, and a second ferromagnetic layer in order from aposition near the current-carrying part.
 16. The spin element accordingto claim 2, wherein the current-carrying part is a magnetic recordinglayer including a magnetic domain wall, and wherein the element partincludes a non-magnetic layer and a first ferromagnetic layer in orderfrom a position near the magnetic recording layer.
 17. The spin elementaccording to claim 5, wherein the first wiring contains a non-magneticmetal having a large atomic number of 39 or more and having d electronsor f electrons in an outermost shell.
 18. The spin element according toclaim 5, wherein the first wiring has a thickness equal to or smallerthan a spin diffusion length of an element constituting the firstwiring.